


The Tomorrow Cross-Z Will Create

by anonyp



Category: Kamen Rider Build
Genre: Gen, Post-Kamen Rider Build, Sento and Banjou's extreme self-sacrificing codependency, draws heavily from Kamen Rider Build: Final Stage, questionable late night grammatical choices, theory framed as character introspection
Language: English
Status: Completed
Published: 2021-01-05
Updated: 2021-01-05
Packaged: 2021-03-16 09:27:54
Rating: General Audiences
Warnings: No Archive Warnings Apply
Chapters: 1
Words: 983
Publisher: archiveofourown.org
Story URL: https://archiveofourown.org/works/28579734
Author URL: https://archiveofourown.org/users/anonyp/pseuds/anonyp
Summary: Sento considers the possibility of Banjou Ryuuga, architect of the world.
Relationships: Banjou Ryuuga & Kiryuu Sento
Comments: 4
Kudos: 12





	The Tomorrow Cross-Z Will Create

**Author's Note:**

> Got curious when a few others in the Cherry Magic discord started watching Build and decided to hop on the bandwagon, and then Best Match boys hijacked my fixation braincell before I’d finished any coherent CM content, whoops.
> 
> Being late to the fandom, I’m not sure if anyone’s discussed this theory or not, but the idea wouldn’t leave me alone. Figured I might as well write it down.
> 
> Not technically a ship fic, but I do ship it and that probably bleeds through.

Ever since Sento awoke in the new world, the question had been on his mind. _How am I here? Why am I here?_ It was quickly sidelined by more pressing concerns (making sure this world was indeed free of Evolt's influence, checking that his friends- his family were alive and well, finding food and shelter for one-and-then-two people with no legal identity), but it remained, an idle thread to be picked up again later.

Later being a time like now, as he huddled next to Banjou in the dark, body exhausted but brain still running on high gear. Banjou was out like a light, breaths slow and even in sleep. That was the other part of the mystery - how could the Banjou he knew, who remembered the old world and one Kiryuu Sento, be here alongside that black-haired stranger who shared his name and face?

Sento's latest hypotheses about their anomalous existence were centered around his companion. Katsuragi and Utsumi had both brought up the possibility that Sento remained as the "creator" of the new world. However, Banjou should have merged with his counterpart, Evolt's genes or no - all of the Riders were subjected to genetic modification in order to transform, if not quite to the same degree, and that hadn’t stopped the others from leaving. Utsumi had literally been turned from a cyborg back into a human. They all saw the doors at the end of that place between realities, but Banjou couldn’t leave through his... Had it even been his? There were two people left at the time, after all. Sento hadn't tried to leave, utterly convinced that he wouldn't have that opportunity. But maybe the door had been his own, or rather Katsuragi Takumi's own (he had never been Satou Tarou, really; he was just forced to borrow a dead man's face).

Pandora's Box was Evolt's power - no matter how inhumanly high Sento's Hazard Level rose, it was still Banjou who needed to be there to harness the Box’s potential. Would it be so strange to think Banjou was the true creator of the new world, however unknowingly? With that idea as a seed, explanations might follow. Perhaps Banjou couldn't leave because the Box was waiting for his touch to finalize the shape of its creation. Perhaps Banjou, in all of his stubborn loyalty, refused to allow the existence known as Kiryuu Sento to vanish. Perhaps Banjou carved a place for his hero to see the world of love and peace he fought for. Perhaps Banjou carved himself a second place beside his hero, because he didn’t want to forget. (And so there were two Banjou Ryuugas in the new world - a truly human one for his beloved Kasumi, who hadn't deserved to be dragged into Evolt's schemes, and one that would not, could not leave Sento behind.)

Sento sighed. He felt… a number of conflicting ways about this conjecture, and the situation in general. Pleased that Banjou would think so highly of him. Frustrated that Banjou wasn't living the war-and-trauma-free life of his double the way Sento had intended. Relieved that he didn't have to be alone with his memories of the old world. Resentful that he had to deal with those memories (and the accompanying guilt) at all when he had been fully ready to go down with Evolt. And then, abruptly: Alarmed that Banjou, as creator, might have remained unmerged regardless of Sento's erasure. Glad that he was here, so _Banjou_ didn't have to be alone. Sento was a genius, had something of an identity unique to himself, and had been resigned to a fate of being forgotten; he figured he could have gotten by on his own. But Banjou? He couldn't imagine the musclehead fending for himself without getting into doppelganger-related trouble or simply breaking under the weight of an entire reality's worth of memories he couldn't share with anyone. Banjou had been so lost in the aftermath of Kasumi’s death. He latched so firmly onto Sento after his life was upended simply because Sento had believed in him... what would happen without that anchor?

> _“Our relationship isn’t about something so simple!”_
> 
> _“If you won’t be with us, then what’s the point?!”_

With a frown, he mentally slammed a door shut on those memories, not wanting to pursue that unpleasant train of thought further. (There was nothing else behind any of the doors in his head besides his own thoughts and memories, now. It was almost a little lonely without Katsuragi there.) He glanced at his partner, gaze tracing what he could make out of Banjou's silhouette. The idiot seemed happy enough to call their presence in the new world another “miracle caused by the power of humanity”. (He probably hadn’t thought about it much. Sento almost envied his simplicity, his freedom from the burning need to _understand_ what exactly they had done. There was a reason Sento was the brains of their outfit, but this phenomenon was beyond even a genius’ grasp of physics.) For the time being, Sento figured he’d keep his theory to himself. He didn’t have any solid proof, and Banjou probably wouldn’t understand it, anyway. It would be simpler to let him continue believing that Sento created the new world and merely brought him along for the ride. If they didn't do as good of a job with saving the world as they hoped, he wouldn't want Banjou to shoulder that guilt.

That veered back toward the depressing territory he was trying to avoid. "This is the worst," he muttered. The words faded into the nighttime silence, and Sento willed his thoughts to fade with them. The Skywall was gone, Evolt was gone, he was alive, and Banjou was by his side. For now, that was enough. That had to be enough. He closed his eyes, hoping sleep would take pity and relieve him of his worries for a few hours.

**Author's Note:**

> wow I finally posted something on ao3 that isn't tourabu
> 
> Quotes based on GenmCorp's subs for Final Stage.


End file.
